| OpendTect Workflows Documentation version 4.2 |
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Purpose: Calculate multi-trace attributes on 2D or 3D seismic by extracting data along seismic events, filter along seismic events, auto-track chrono-stratigraphic horizons (SSIS plugin), and to compute attributes based on local dip-azimuth information only.
Theory: If we know, at each position in a 3D volume, the direction (dip-azimuth) of the seismic events we can use this information to create a local horizon at each position in the cube simply by following the dip and azimuth information from the center outwards. We call this process dip-steering. It requires a pre-calculated steering cube and is used to compute better (dip-steered) attributes and to filter the data. In addition, the steering cube can be used to create various attributes that are purely based on dip-azimuth information. For example curvature attributes but also the dip in the inline and crossline direction. Lastly the dip-steering process is used to auto-track chrono-stratigrpahic horizons in the SSIS plugin. We often use two versions of the steering cube: detailed and background. Detailed steering cube is the cube that is computed with the default settings. It is primarily used for attribute calculations. The background steering cube is a heavily smoothed (e.g. median filtered 4x4x4) version of the detailed steering cube. Its main use is in dip-steered filtering of seismic data.
Software: OpendTect + Dip-Steering (+ SSIS)
Workflow:
- Create a Detailed Steering Cube (Processing - Steering - Create, e.g. FFT 3x3x3).
- Create a Background Steering Cube (Processing - Steering - Filter, e.g. 4x4x4).
- Open the Attribute Set Window and add new attributes from the Steering Cube (Dip, Curvature), or that use Steering - Full option where applicable. Examples: Similarity, Volume Statistics (median filter).
- Apply the attributes to the seismic data in batch: Processing - Create seismic output, or on-the-fly: right-click on the element in the tree (e.g. part of a time-slice).
Tips:
- To QC the Steering Cubes: create a Crossline dip attribute (Dip attribute) from the Detailed Steering Cube and from the Background Steering Cube and display both on an inline.
See also chapter 3.2 - dip-steered median filter